1) Is it recommended to use the XLR output of CP73 to the MIC inputs of my mixer or is it better to use the Line level outputs for the CP73?

The CP73 is not a Mic. The CP73 is Line level. Can you hear your mixer screaming? A microphone (invented by Alexander G. Bell in the 1870s works with a very tiny, tiny magnet mounted on a tiny diaphragm (like an ear drum). When sound waves (air molecules in motion) hit the diaphragm, it moves the tiny magnet back an forth in between a coil of copper wires, this causes a very tiny amount of electricity to flow. The output is very very very small.

Mic inputs on a mixer general have a Gain Control (pre amplifier) that is used to boost that signal. The tiny tiny amount of signal must be amplified (a whole bunch) by the mixer channel’s pre-amp so that the mixer channel can send it on... to an amplifier.

The CP73 is a Line level signal... so much more powerful than the small magnet in coil of copper wire, that it’s not funny. The CP73 draws voltage from your house wall socket and puts that to work. The signal coming from the CP73 is so much more powerful compared to the tiny amount of voltage created by that tiny little magnet... it ain’t funny. Just connecting it causes a tremendous amount of HISS... Thing of hiss as the enemy, it’s a warning (like a rattle snake, so back off, completely!)

Comparison: you filling your mouth with water and then forcing it through a straw. Yes, you get a stream of water coming out... that’s your mic level.
Now a fire truck pulls up and the fireman connects the hose to a hydrant and forces a stream of water through the fire hose... that's your Line level signal coming from the CP73.

So you plug a Line level device (CP73) into an input prepared for a weak microphone signal. That noise you hear is the TOO MUCH signal entering the mixer channel. Don’t do that! You can damage your mixer channels electronics!!!

You don’t mention what the name of this (poor) mixer. Hopefully, you have not permanently damaged it.
Some mixers have a switch that says Mic/Line on the channel. Understand “Mic” is for weak low level signals (like a dynamic microphone)... “Line“ switches the input by padding the incoming signal so as not to damage the electronics of the mixer channel. “Line” is for signals that don’t need so much help from your mixer.

Microphones, like the Shure SM58, output signal at a low level, typically -52dB or there about.
Keyboard, like the CP73 output signal at 0dB or even +6dB. Many, many times more powerful.

If you do not have a button on the mixer channel that allows you to select between MIC/LINE, then you cannot use XLR cables from your keyboard to that mixer. You are better off using standard 1/4” cables to connect your CP73 to two channels of the mixer — one for Left Output, the other for Right Output.

2) On a separate note, I'm interested to use the CP73 as a midi controller. Do I use the MIDI IN and OUT or do I use the USB to host? Can someone help me out here?

It depends on what you are intending to control. MIDI can travel through either the 5-pin MIDI jacks or it can travel through the USB cable when you are connecting to a computer or tablet ‘host’ device. Inside the MENU List setting of the CP73 you can turn On MIDI for the connection you choose to use

MIDI Out from the CP can be used when connecting to another synthesizer.
The USB for MIDI would be used when connecting to a computer.
Unfortunately, you don’t tell us what you wish to control

p.s: I'm using an AES/EBU cable for the XLR output not sure if that affects / contributes to hissing.

What are you doing with an AES/EBU cable? The hissing as explained is your mixer screaming: “HELP! Aim that fire hose somewhere else!”

I’m keeping it light... but seriously you can damage your gear plugging things up improperly.

When you want good info, supply as much info as you can. Your mixer may be able to handle LINE level signals (CP73) BUT again unfortunately, you give us no information on the mixer... but no mixer channel set to “Mic” Input is going to handle that powerful “Line” level input coming from the CP73. Consider that hiss your mixer channel Screaming!!! Because TOO MUCH signal is pouring in.

Hi,

Thanks for the quick reply. I have disconnected the AES/EBU cable from the CP73. The mixer is a Yamaha MW12C 12-Channel USB Mixer that I'm "experimenting" with. I didn't know that I could damage the electronics that way. I also used an AES cable that I plugged out from my audio system as I don't have an XLR on hand. Anyway, I'll change it to a 1/4 inch instrument cable. I don't think the Yamaha mixer has a setting to change the MIC input to Line.

I'm actually trying to hook up the CP73 as a midi controller to Cubase so that I can use different VSTs. When you say USB for MIDI you mean like a cable with 5 pin DIN on one end and USB on the other end? Can I just connect USB to host to my computer and use it as a MIDI controller? And also what's USB to Device?

I hope it's clearer now what I'm trying to achieve, I'm still learning so maybe some of my questions may not make sense. Thanks for the help.

The mixer is a Yamaha MW12C 12-Channel USB Mixer that I'm "experimenting" with.

Connect your YC61 with two standard 1/4” cables — use the stereo channels 5/6 or 7/8

Connect the YC Left Output to the odd numbered channel input and the YC Right Output to the even numbered channel input.
Connect both Left and Right channels. You have two ears... music should always be listened to in STEREO... you need two ears to hear stereo. Stereo is better than Mono. Be sure to connect the Left Output of the Mixer and the Right Output of your mixer, or use Headphones (notice they come with a speaker for each of your ears ... to maintain STEREO and to enhance the enjoyment of music).

I didn't know that I could damage the electronics that way.

Only plug microphones into the XLR jacks labeled MIC. Remember the fire hose story (told to leave an impression)... you wouldn’t want to drink from a fire hose!! Yes, it can do damage!

I'm actually trying to hook up the CP73 as a midi controller to Cubase so that I can use different VSTs. When you say USB for MIDI you mean like a cable with 5 pin DIN on one end and USB on the other end?

No, I mean a standard USB cable (like used to connect a printer to a computer). You are going to be connecting the YC61’s “USB TO HOST” port to your computer via a standard USB cable.

Please see “Connecting to a computer” page 29 of your Owner’s Manual (pictures are worth a thousand words).
You will need to download and install the “Yamaha Steinberg USB Driver version 2.0.3” for your particular computer type, Mac or Windows.

The computer is the “host”... it will be ‘entertaining‘ your YC61 which is the guest coming over to visit. You don’t mention what type of computer... you may have to get an adapter (new Macs require lots of adapters... ). The sound of the YC61 and the sound of any VSTi you are going to be controlling will be coming out of the YC61... it acts as an audio interface for your computer.

You will also want to look up in the Owner’s Manual how to turn “Local Control” = Off (Page 38) this allows you disconnect the YC keyboard from the YC tone engine... letting you determine what you hear by Routing settings in your computer.

And also what's USB to Device?

The YC61 USB “TO DEVICE” port allows you connect a USB stick (storage) where you can Save your YC Live Set programs.
Page 20:
“For connecting a USB flash drive to this instrument, allowing you to use the device to save data you have created and load data you want to restore.”

Let us know.